Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to the prevention of chemical or biological attacks on building air circulation systems. More specifically, the invention comprises a detection system which isolates contaminants to prevent their circulation within a building.
2. Description of the Related Art
It is well known that particulate contamination of a gas will cause the attenuation of a light beam traveling through the gas. As one example, U.S. Pat. No. 5,766,956 to Groger, et al. (1998) discloses the use of a diode laser emitter to detect the presence of chemical or biological agents. The attenuation resulting from the presence of a particular contaminant also varies with the wavelength of the light used. FIGS. 5 through 7 in the ""956 disclosure illustrate this phenomenon. It is thus known that certain wavelengths of lights are particularly useful for detecting certain classes of substances.
Optical detection systems have become increasingly sophisticated, with an emphasis on eliminating false alarms caused by ambient lighting and contaminant accumulation on the optical surfaces of the device. One example of such a sophisticated detection system is found in U.S. Pat. No. 5,946,092 to DeFreez, et al. (1999). It is also known to combine different types of sensors to eliminate false alarms. This is particularly true in the field of fire detection. U.S. Pat. No. 5,945,924 to Marman, et al. (1999) teaches the combination of a particle sensor with a carbon dioxide sensor to eliminate false alarms.
Practically all optical sensors suffer degraded performance over time. This results from the fact that the optical surfaces become dusty with use. If a fixed level of attenuation is used to trigger the detector, this level may be reached by the accumulation of dust. Frequent cleaning is one remedy for this problem. However, techniques have evolved to permit the adjustment of the trigger threshold over time. One such approach is disclosed in U.S. Pat. No. 6,107,925 to Wong (2000). The Wong device adjusts its trigger threshold to account for dust contamination over time.
The events of 2001 have raised concerns regarding biological and chemical attacks on commercial buildings. Most such buildings have external intakes for their HVAC systems. Many of these intakes are in exposed positionsxe2x80x94in parking garages or along the streets. If a chemical or biological agent is introduced into the HVAC system, the system will quickly circulate the contaminant throughout the building.
U.S. Pat. No. 6,217,441 to Pearman, et al. (2001) discloses a gas-activated seal which can restrict the flow of air through a duct. Many other prior-art devices are available to shut off flow through a duct. However, the prior art devices have not combined a contaminant sensor with a control to isolate the spread of the contaminant.
The known devices are therefore limited in that although they are capable of detecting contaminants, they do not contain and isolate the contaminant.
The present invention comprises an apparatus for detecting and containing chemical or biological contaminants. The invention includes one or more optical contaminant detectors, capable of detecting chemical and biological agents. A containment assembly is installed in the duct work of a building, just downstream from the main intake. Air flows linearly through the containment assembly. The air first flows through a first damper, then through the contamination sensor or sensors, and then through a second damper.
If a sensor senses a contaminant, a controller shuts off the HVAC system, while simultaneously closing the first and second dampers. The containment assembly is thereby hermetically sealedxe2x80x94trapping any contaminants inside. The sensors and second damper are spaced sufficiently far apart so that no contaminant will flow through the second damper before its closure. The controller can also be configured to alert authorized personnel as to the potential contamination.
Accordingly, several objects and advantages of the present invention are:
1. To detect chemical or biological contaminants in an air duct;
2. To shut off the building HVAC system in response to an attack;
3. To alert the appropriate persons regarding the existence of an attack; and
4. To contain any contaminants already in the air duct in such a fashion that they cannot escape.